Re: [PATCH 2/4] mtd: spi-nor: Add support for Octal 8D-8D-8D mode

[masonccyang]

Hi Vignesh,


> >> On 15/11/19 2:28 pm, Mason Yang wrote:
> >>> According to JESD216C (JEDEC Basic Flash Parameter Table 18th DWORD)
> >>> Octal DTR(8D-8D-8D) command and command extension (00b: same, 01b: 
> > inverse)
> >>> to add extension command mode in spi_nor struct and to add write_cr2
> >>> (Write CFG Reg 2) for 8-8-8/8D-8D-8D mode sequences enable.
> >>>
> >>
> >> But I don't see any code setting "nor->ext_cmd_mode" based on BFPT?
> >>
> >> Any new feature that we add to spi-nor should make use of 
autodiscovery
> >> feature made possible by SFDP tables. Could you modify the patch to
> >> discover capabilities supported by flash and opcodes to be used from
> >> SFDP table?
> > 
> > Got it but our device will return a empty SFDP table.
> > 
> 
> If flash you tested on does not support JEDEC 216C then don't mention
> about it. Above commit message gives an impression that flash in JEDEC
> 216C compliant.
> 

okay, got it.

> >>
> >>
> >>> Define the relevant macrons and enum to add such modes and make sure
> >>> op->xxx.dtr fields, command nbytes and extension command are 
properly
> >>> filled and unmask DTR and X-X-X modes in 
> > spi_nor_spimem_adjust_hwcaps()
> >>> so that DTR and X-X-X support detection is done through
> >>> spi_mem_supports_op().
> >>>
> [...]
> >>> @@ -404,6 +436,30 @@ static int read_sr(struct spi_nor *nor)
> >>>                 SPI_MEM_OP_NO_DUMMY,
> >>>                 SPI_MEM_OP_DATA_IN(1, nor->bouncebuf, 1));
> >>>
> >>
> >> This is not based on the latest tree.
> >>
> >>> +      if (spi_nor_protocol_is_8_8_8(nor->read_proto)) {
> >>> +         op.cmd.buswidth = 8;
> >>> +         op.addr.buswidth = 8;
> >>> +         op.dummy.buswidth = 8;
> >>> +         op.data.buswidth = 8;
> >>> +         op.cmd.nbytes = 2;
> >>> +         op.addr.nbytes = 4;
> >>> +         op.dummy.nbytes = 4;
> >>> +         op.addr.val = 0;
> >>
> >> This is not scalable... There will be bunch of if...else ladders when 
we
> >> want to support other X-X-X modes... Can't these be derived from
> >> nor->reg_proto? And then borrow the logic from 
> > spi_nor_spimem_read_data()?
> >>
> > 
> > Got it !
> > 
> >>
> >> Could you have a look at Boris's initial submission to add 8-8-8 mode 
at
> >> https://patchwork.kernel.org/cover/10638055/ ?
> >> You could use that series as the base for your changes/additions.
> > 
> > Got it.
> > My idea is to support 8D-8D-8D mode with a minimum patches because 
> > there is no define for 1D-1D-1D, 2D-2D-2D and 4D-4D-4D mode in JEDEC 
> > if I am right.
> > 
> 
> JESD251-A1 does talk about 4S-4D-4D right? Also none of the JEDEC
> standards prohibit flash vendors from supporting other X-X-X modes.
> 
> I think you haven't thought about bigger picture here. Flash devices
> that support other mode exist today and we would need the framework to
> be built such that these modes can be added in future.
> 
> I suggest you start with Boris's series [1] as base and port it to
> latest kernel. Isn't that series alone enough to support Macronix Octal
> flashes at least?
> If required, you could also always include additional patches adding new
> features.

okay.

> 
> [1] https://patchwork.kernel.org/cover/10638055/
> 
> -- 
> Regards
> Vignesh

thanks for your time & comments.
Mason

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